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<div class="titlepage"><div><div><h3 class="title">
<a name="boost_typetraits.reference.is_convertible"></a><a class="link" href="is_convertible.html" title="is_convertible">is_convertible</a>
</h3></div></div></div>
<pre class="programlisting"><span class="keyword">template</span> <span class="special">&lt;</span><span class="keyword">class</span> <span class="identifier">From</span><span class="special">,</span> <span class="keyword">class</span> <span class="identifier">To</span><span class="special">&gt;</span>
<span class="keyword">struct</span> <span class="identifier">is_convertible</span> <span class="special">:</span> <span class="keyword">public</span> <em class="replaceable"><code><a class="link" href="integral_constant.html" title="integral_constant">true_type</a>-or-<a class="link" href="integral_constant.html" title="integral_constant">false_type</a></code></em> <span class="special">{};</span>
</pre>
<p>
        <span class="bold"><strong>Inherits:</strong></span> If an imaginary rvalue of type
        <code class="computeroutput"><span class="identifier">From</span></code> is convertible to type
        <code class="computeroutput"><span class="identifier">To</span></code> then inherits from <a class="link" href="integral_constant.html" title="integral_constant">true_type</a>,
        otherwise inherits from <a class="link" href="integral_constant.html" title="integral_constant">false_type</a>.
      </p>
<p>
        Type From must not be an incomplete type.
      </p>
<p>
        Type To must not be an incomplete, or function type.
      </p>
<p>
        No types are considered to be convertible to array types or abstract-class
        types.
      </p>
<p>
        This template can not detect whether a converting-constructor is <code class="computeroutput"><span class="keyword">public</span></code> or not: if type <code class="computeroutput"><span class="identifier">To</span></code>
        has a <code class="computeroutput"><span class="keyword">private</span></code> converting constructor
        from type <code class="computeroutput"><span class="identifier">From</span></code> then instantiating
        <code class="computeroutput"><span class="identifier">is_convertible</span><span class="special">&lt;</span><span class="identifier">From</span><span class="special">,</span> <span class="identifier">To</span><span class="special">&gt;</span></code>
        will produce a compiler error. For this reason <code class="computeroutput"><span class="identifier">is_convertible</span></code>
        can not be used to determine whether a type has a <code class="computeroutput"><span class="keyword">public</span></code>
        copy-constructor or not.
      </p>
<p>
        This template will also produce compiler errors if the conversion is ambiguous,
        for example:
      </p>
<pre class="programlisting"><span class="keyword">struct</span> <span class="identifier">A</span> <span class="special">{};</span>
<span class="keyword">struct</span> <span class="identifier">B</span> <span class="special">:</span> <span class="identifier">A</span> <span class="special">{};</span>
<span class="keyword">struct</span> <span class="identifier">C</span> <span class="special">:</span> <span class="identifier">A</span> <span class="special">{};</span>
<span class="keyword">struct</span> <span class="identifier">D</span> <span class="special">:</span> <span class="identifier">B</span><span class="special">,</span> <span class="identifier">C</span> <span class="special">{};</span>
<span class="comment">// This produces a compiler error, the conversion is ambiguous:</span>
<span class="keyword">bool</span> <span class="keyword">const</span> <span class="identifier">y</span> <span class="special">=</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">is_convertible</span><span class="special">&lt;</span><span class="identifier">D</span><span class="special">*,</span><span class="identifier">A</span><span class="special">*&gt;::</span><span class="identifier">value</span><span class="special">;</span>
</pre>
<p>
        <span class="bold"><strong>C++ Standard Reference:</strong></span> 4 and 8.5.
      </p>
<p>
        <span class="bold"><strong>Compiler Compatibility:</strong></span> All current compilers
        are supported by this trait.
      </p>
<p>
        <span class="bold"><strong>Header:</strong></span> <code class="computeroutput"> <span class="preprocessor">#include</span>
        <span class="special">&lt;</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">type_traits</span><span class="special">/</span><span class="identifier">is_convertible</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">&gt;</span></code>
        or <code class="computeroutput"> <span class="preprocessor">#include</span> <span class="special">&lt;</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">type_traits</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">&gt;</span></code>
      </p>
<p>
        <span class="bold"><strong>Examples:</strong></span>
      </p>
<div class="blockquote"><blockquote class="blockquote"><p>
          <code class="computeroutput"><span class="identifier">is_convertible</span><span class="special">&lt;</span><span class="keyword">int</span><span class="special">,</span> <span class="keyword">double</span><span class="special">&gt;</span></code> inherits from <code class="computeroutput"><a class="link" href="integral_constant.html" title="integral_constant">true_type</a></code>.
        </p></blockquote></div>
<div class="blockquote"><blockquote class="blockquote"><p>
          <code class="computeroutput"><span class="identifier">is_convertible</span><span class="special">&lt;</span><span class="keyword">const</span> <span class="keyword">int</span><span class="special">,</span> <span class="keyword">double</span><span class="special">&gt;::</span><span class="identifier">type</span></code>
          is the type <code class="computeroutput"><a class="link" href="integral_constant.html" title="integral_constant">true_type</a></code>.
        </p></blockquote></div>
<div class="blockquote"><blockquote class="blockquote"><p>
          <code class="computeroutput"><span class="identifier">is_convertible</span><span class="special">&lt;</span><span class="keyword">int</span><span class="special">*</span> <span class="keyword">const</span><span class="special">,</span> <span class="keyword">int</span><span class="special">*&gt;::</span><span class="identifier">value</span></code> is an integral constant expression
          that evaluates to <span class="emphasis"><em>true</em></span>.
        </p></blockquote></div>
<div class="blockquote"><blockquote class="blockquote"><p>
          <code class="computeroutput"><span class="identifier">is_convertible</span><span class="special">&lt;</span><span class="keyword">int</span> <span class="keyword">const</span><span class="special">*,</span> <span class="keyword">int</span><span class="special">*&gt;::</span><span class="identifier">value</span></code> is an integral constant expression
          that evaluates to <span class="emphasis"><em>false</em></span>: the conversion would require
          a <code class="computeroutput"><span class="keyword">const_cast</span></code>.
        </p></blockquote></div>
<div class="blockquote"><blockquote class="blockquote"><p>
          <code class="computeroutput"><span class="identifier">is_convertible</span><span class="special">&lt;</span><span class="keyword">int</span> <span class="keyword">const</span><span class="special">&amp;,</span> <span class="keyword">long</span><span class="special">&gt;::</span><span class="identifier">value</span></code>
          is an integral constant expression that evaluates to <span class="emphasis"><em>true</em></span>.
        </p></blockquote></div>
<div class="blockquote"><blockquote class="blockquote"><p>
          <code class="computeroutput"><span class="identifier">is_convertible</span><span class="special">&lt;</span><span class="keyword">int</span><span class="special">,</span> <span class="keyword">int</span><span class="special">&gt;::</span><span class="identifier">value</span></code>
          is an integral constant expression that evaluates to <span class="emphasis"><em>true</em></span>.
        </p></blockquote></div>
<div class="blockquote"><blockquote class="blockquote"><p>
          <code class="computeroutput"><span class="identifier">is_convertible</span><span class="special">&lt;</span><span class="identifier">T</span><span class="special">,</span> <span class="identifier">T</span><span class="special">&gt;::</span><span class="identifier">value_type</span></code>
          is the type <code class="computeroutput"><span class="keyword">bool</span></code>.
        </p></blockquote></div>
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